Devices which produce drag or damping by means of either friction or viscous shear between relatively moving elements are known. The former typically comprise a friction clutch, attached to one element and contacting the relatively moving element under pressure, such that energy is dissipated by the resulting sliding contact. The magnitude of the damping force is dependent upon the friction contact pressure and is readily varied.
The torque/speed characteristic of a friction damper may be modified by the choice of friction materials and/or the provision of a fluid at the friction surface to provide boundary lubrication of the sliding contact in which case the damping force may rise with increasing speed from an initial stationary position and thereafter remain substantially constant irrespective of speed.
Viscous dampers typically comprise multiple interleaved plates alternately attached to each of the relatively moving elements, each plate being separated from adjacent plates by a small gap occupied by a viscous fluid. Relative movement of the plates causes viscous shear to take place in the fluid. The damping force generated, tends to increase substantially linearly with speed but at rest is zero.
One particular and important application of drag/damper devices is in pan and tilt heads for cameras, especially television cameras. In this application it is advantageous, to avoid "jerking" when making very slow camera movements from rest, for the torque to be substantially zero at near zero speed. On the other hand, for increasingly fast camera movements above a certain speed, it is advantageous for the torque not to become increasingly high.
In applications such as camera mounting, where the purpose of the damping device is to enhance the smoothness and control of manual movements, the following characteristics are therefore desirable:
1. The rate of change of the damping/speed relationship should tend to zero an high speed to permit relatively fast movements to be accomplished without unreasonable restraint, whilst providing adequate damping control at low speeds. PA0 2. For fine control at the commencement of movement and during reversals, the unit should produce zero damping at rest and a high rate of change of damping with speed at low speeds.
It is a general object of this invention to provide a drag/damper unit which possesses these characteristics.
It is another object of the invention to provide an improved pan/tilt head for a camera mounting, which possesses the above characteristics.
Preferably the amplitude of any damping is variable.
It is a further object of the invention to produce a drag/damper unit (and/or a pan/tilt camera mounting head) in which the amplitude of damping is infinitely variable between limits.